Sci came across this abstract via NCBI ROFL, the aggregation site with some truly hilarious studies on it, many of them worthy Friday Weird Science materials. And of course this one is EXTRA worthy. It’s from the Journal of Medical Hypotheses. Wither Weird Science, Medical Hypotheses, but for thee?
So, coming up into this next week, Sci is proud to announce an awesome series of guest posts. Seeing as we spent the last three weeks or so on female reproduction, it seems only fair to represent the other side of the coin, and so, for this next week, we’ll be covering the basics of male reproduction, courtesy of the awesome and brilliant Ambivalent Academic.
And what a way to get into it… Kumar and Kumara. “Swinging high and low: Why do the testes hang at different levels? A theory on surface area and thermoregulation” Medical Hypotheses, 2008.

As I’m sure many of you are aware, most guys have two testicles. In fact, almost ALL guys have two testicles. The testicles are up in the abdominal cavity as a fetus, and descend to hang below the abdominal cavity after birth. In some men (I’ve heard as high as 10%, but until I have a ref for that it’s just anecdotal) one testicle will not descend, and so some guys have what looks like just one, and I don’t believe there’s a negative effect on fertility there.
There are three possible positions for the testicles once descended: hanging equally, the right one hanging higher, or the left one hanging higher. It’s common knowledge that a lot of guys have one testicle that hangs slightly lower than the other. Some say that this goes with handedness, and if you’re right handed your right testicle will be higher, but I think that’s pretty silly. Approximately 21% of men are thought to have the right testicle lower, 27% hang equally, and I suppose if you assume 10% only have one, that leaves 42% with the left testicle hanging lower (the first two numbers are from this pdf, which I think is hilarious and might have to be blogged).
So the question is: WHY do a lot of men’s testicles hang unevenly? There have been lots of hypotheses proposed for this: differences in embryonic development, vascular differences, evolutionary differences. But these authors came up with a different hypothesis: temperature!
So what does temperature have to do with your balls? Well, as guys probably know from encounters with things like cold showers, testicles are very sensitive to temperature.
Your testicles are sensitive to temperature because sperm development requires a slightly lower temperature than the 98.6 degrees Fahrenheit in your body. Hence, the testicles are suspended below the abdominal cavity, in order to have the right temperature at which to make the little swimmers we all know and love.
As to why one testicle might hang lowER, the authors propose that it is yet again due to temperature. When the balls hang at the same height, they reason, the inside surfaces of them are pressed together, and this might mean that it’s too hot in there. only the outside surfaces would be at the right temperature to produce sperm. Whereas, if one of the boys hangs lower, much more of that testicle would be exposed to the air, meaning it might have better temperature conditions in which to do its job.
Of course, this is a hypothesis. But there could be some cool ways to test this. I say, find guys with equal balls, and guys with one hanging lower, put them all in a room where the temp is equal and they have plenty of time to adjust to the room temperature. Measure the temperatures of each ball, and then check the viable sperm count of the dudes. If the lower hanging ball is indeed cooler, and those guys have higher sperm counts, you might be able to draw a correlation. Pretty easy to test, really. Additionally, you could get some data from guys going in for fertility treatment and low sperm counts. Do an overwhelming number of them have even hanging balls?
While Sci thinks that this hypothesis proposed above is not unlikely, and is something actually could probably be tested, she’s not sure it’s the right answer. My thought is that, if having testicles where one needs to hang lower confers a significant reproductive advantage (better sperm, obviously) when mating, then it doesn’t explain the large number of men who apparently have equal hanging testicles. If the lower hang is important for increased function, those guys with equal hanging testicles would have been out-bred by now. So while I think the temperature hypothesis might be part of the reason, and might confer some advantage, I don’t think it’s the main reason.
Sci has…another hypothesis. Her hypothesis is space. This hypothesis actually might be good fodder for the Journal of Medical Hypotheses! (Who knows, perhaps Sci should publish there just for fun…) I am constantly hearing from various guys that their junk takes up space. Evidence of this can be found in the fact that guys always tend to sit like this on subways:
(Honestly guys, make some room! What do you have between there, the Eiffel tower?! Yeesh. I only wish I had Isis’ skills with photoshop to make this photo that much more evocative…)
So yeah, dude’s junk takes up space. They are constantly adjusting it, holding it up, pulling it around, etc. And it’s true, between an average guy’s legs there’s really not a lot of space. Those balls are squished in there. So it is Sci’s hypothesis that it’s merely space that requires one ball to hang lower than the other, and that this is probably individual and not a genetically determined kind of thing (though who knows, really).
But of course, to get to the bottom of this, we have to do the experiment!!! Who’s in?!KUMAR, A. (2008). Swinging high and low: Why do the testes hang at different levels A theory on surface area and thermoregulation Medical Hypotheses, 70 (3), 698-698 DOI: 10.1016/j.mehy.2007.06.023

Yep, my own lefty hangs just a bit lower. Your space hypothesis seems likely to me, but not quite for the same reasoning. My testes can, and do, damned near fully retract into my body under certain circumstances, and with the slight offset the full width of both testicles doesn’t have to get through there, in which case I imagine they’d simply remain more exposed.
Perhaps ancestors that inherited this trait were somewhat less likely to suffer scrotal injury at the hands of violent persons places or things? Just enough of a pressure to make it prevalent without it being a requirement for propagation?
I think it’s also always important to consider that a trait is simply not inconvenient enough to be weeded out. Like buck teeth or blonde hair.
Also, we sit like that because, as you should be able to guess, it provides some welcome airflow and easy hand access to The Region.

Actually, in an A&P class I took, I learned a few neat little tidbits:
When it gets warmer, the separation between the two testicles increases, lending support to the temperature hypothesis.
If one’s legs are closer together, however, the distance increases more, lending support to the space hypothesis-if this were only the case in humans.
Many male mammals, however, have the same thermoregulatory scrotum, and on all of the ones I am familiar with, space is certainly not an issue. If anyone cares to analyze quadrupedal placental mammals with a scrotum to see if one hangs lower than the others. Such an observation would disprove the space hypothesis. If, however, they are found to hang evenly, it would disprove the temperature hypothesis.

But hang on, this is just bollocks. They’re always on the move. Over a span of time, one is slowly creeping up, the other slowly but not necessarily in sync, creeping a bit further down, like a lava lamp or a background effect from the seminal ‘60’s film “Barbarella”. It more or less comes down to when exactly you sample the position. I wouldn’t consider it true to claim that there are men who have equally hanging balls all the time — even those will make minor traversal journeys up and down a bit, independently.

So, Ian @ 5, what you are saying is that there is something like indeterminacy in the testicular field, and that we should only be speaking of the probability of finding testicles in certain locations. (I certainly hope the probability density is entirely confined to the scrotum. I wouldn’t like to find out what it is like to suddenly experience on testicle being across the room or somewhere in Denmark momentarily.)

Additionally, you (well, I) can make them move further up or down a bit if you concentrate on them — not by muscular “hoisting” but more through focusing relaxation at them and giving them ages to decide to respond. But my findings this morning result in the conclusion that my left one can go lower or higher than my right one, which was defaulting to a lower position before I started. Maybe they do have “resting positions” but there’s a lot of other factors that could be affecting their instantaneous positioning at any given window of observation.

I blame pants! The way that pants are designed is such that the seam pushes up right into the middle of everything. The penis (if wearing boxers like I do) needs to fall somewhere and I happen to let it fall to the left. The left testicle hangs lower to get away from the extra heat (remember the best way to warm up someone who is suffering from hypothermia is skin to skin contact?). The right testicle is pushed up by the seam in the shorts and by the pants.
Therefore, with their short-cut crotch design, modern pants suck! Much to my fashionista wife’s disgust, I have trouble finding stylish pants, i.e., the crotch is cut too short and the seam pushes up so far that I am constantly having to adjust (beyond the fact that short crotches provide a bit too much exposure of the unruly design underneath the fabric).
Any studies on whether aborigines who don’t wear underwear or pants have the same hang imbalance? This might assist or shoot down my theory…

Another (null?) hypothesis:Relative position doesn’t matter at all (i.e. no significant ultimate/evolutionary cost or benefit), and it can all be well explained by the net forces created by the scrotum (which is capable of quite a range of shrinkage-here and stretching-there) and whatever other forces each testicle experiences. This includes forces on one another, their relative size/mass/density, and the rest of the plumbing inside the scrotum, etc.
In any case, it seems an important baseline for any empirical study is to understand the basic (known) mechanics of testicle positioning. Then go and worry about whether or not relative positioning (in reality) deviates from what you’d expect, and if those deviations can be better explained by other mechanisms like simultaneous temperature regulation, compensation to avoid physical injury, etc.
Hmmm… maybe someone should send this blog post to the Kinsey Institute?😉

I was born with both testicles undecended and it wasn’t corrected until I was about 7 years old. Each one was done separately, about 6 months apart, but I don’t like the way the surgeon positioned them. They don’t hang low enough and are too close together. My right is slightly lower but they’re still practically level. I definitely need more space down there.

You mean some men actually have symmetrical balls? My right hangs like a full 2″ lower than my left at most times — what a mess! lol And like somebody said above, jeans aren’t made for long hanging balls, so my junk is always balled up (pun intended) and hurtin’. Personally, I wish thems bastards had never even descended!

Testicles are less likely to get squeezed or banged against each other if they are hanging at different heights – for instance, while running. They take up less horizontal space when hanging one on top of the other. So, guys whose balls hang at the same height may be more susceptible to testicle injury, and therefore less likely to reproduce.

But Chuck, anatomically, they are in two separate sacks, and not held by the scrotal skin itself, but suspended by muscles from the body which are also (very loosely) attached to those same muscles, thus your analogy of apples in a bag is not accurate.

Years ago, when I was in Peace Corps, my neighbor let me in on what the Paraguayan campesinos called the increasingly present Mormon missionaries:
The testicles.
They come in pairs, and one is always shorter than the other.

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